I'd prefer a tags system (like guildleves) for the content with have now (8 ppl, 30-60 mins). Cooldown means that if you have a party that can play for 2-3h, you have to fill this time with different fights, moving from one place to another (slight waste). And if there is a (new) player in your party who doesn't have access to every content yet, it gets worse.
(or you just disband after the first win. big waste :| )
Cooldown also means that if my linkshell is planning to do X content this evening, I can't do it during the afternoon even if there is this interesting /shout.

I think cooldown is better suited for content that actually last 2-3h.